Typically, the estimated yield farming returns are calculated annualized. This estimates the returns that you could expect over the course of a year.
Some commonly used metrics are Annual Percentage Rate (APR) and Annual Percentage Yield (APY). The difference between them is that APR doesn’t take into account the effect of compounding, while APY does. Compounding, in this case, means directly reinvesting profits to generate more returns. However, be aware that APR and APY may be used interchangeably.
It’s also worth keeping in mind that these are only estimations and projections. Even short-terms rewards are quite difficult to estimate accurately. Why? Yield farming is a highly competitive and fast-paced market, and the rewards can fluctuate rapidly. If a yield farming strategy works for a while, many farmers will jump on the opportunity, and it may stop yielding high returns.
As APR and APY come from the legacy markets, DeFi may need to find its own metrics for calculating returns. Due to the fast pace of DeFi, weekly or even daily estimated returns may make more sense.